Chapter 12
316 MIPS R4000 Microprocessor User's Manual
External Read Request
In contrast to a processor read request, data is returned directly in
response to an external read request; no other requests can be issued until
the processor returns the requested data. An external read request is
complete after the processor returns the requested word of data.
The data identifier (see System Interface Commands and Data Identifiers
in this chapter) associated with the response data can signal that the
returned data is erroneous, causing the processor to take a bus error.
NOTE: The processor does not contain any resources that are
readable by an external read request; in response to an external read
request the processor returns undefined data and a data identifier
with its Erroneous Data bit, SysCmd(5), set.
External Write Request
When an external agent issues a write request, the specified resource is
accessed and the data is written to it. An external write request is complete
after the word of data has been transmitted to the processor.
The only processor resource available to an external write request is the
Interrupt register.
External Invalidate Request
When an external agent issues an invalidate request, the specified resource
is accessed and the line is marked invalid. An external invalidate request
is considered to be complete after the request has been transmitted.
External Update Request
When an external agent issues an update request, the specified resource is
accessed and the line is replaced. An external update request is
considered complete after the request has been transmitted.
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